based onberg, e.p. & sj ors, arxiv:0912.1341 (hep-th ...mctp/sciprgpgs/events/2011... ·...

Dante’s Inferno

based on Berg, E.P. & Sjors, arXiv:0912.1341 (hep-th)Enrico Pajer

Cornell University

Outline

1 Motivations

2 Dante’s Inferno: the EFT story

3 Dante’s Inferno: the string theory story

4 Conclusions

Enrico Pajer (Cornell) Dante’s Inferno 2 / 22

Outline

1 Motivations



4 Conclusions


Tensor modes and the Lyth bound

The detection of tensor modes would fix the scale of inflation closeto the GUT scale.

Measuring tensor modes puts a lower bound on the range ofvariation of the inflaton [Lyth 98]

dφ

Mpl= dN

√2ε ' dN

√r

8

∆φ

Mpl>

√r

0.01

NCMB

30

∆φ above the cutoff makes the use of EFT suspicious

This is the main motivation to consider axion monodromy inflation

Schematically

Tensormodes

⇒ Highscale

⇒ Largefield

⇒ moreUV-sensitive


UV-sensitivity

EFT approach: learn about higher scales studying UV-sensitiveobservables.

Inflation is a UV-sensitive mechanism. Schematically

V (φ) =1

2m2φ2 +

∑n

λnφn

Mn−4pl

Within string theory and supergravity many models suffer from anη-problem.

We need to invoke a symmetry, e.g. shift symmetry.

Then we need a fundamental theory (UV-finite) to ask if, how andwhere the symmetry is broken.


Axions in field theory and string theory

Axions are scalars with only derivative couplings.

Arise from breaking of a U(1) [Peccei & Quinn 77] or in dimensionalreduction integrating p-forms on p-cycles

c(x) =

∫Σp

Cp , b(x) =

∫Σ2

B2

Continuous shift symmetry at all orders in perturbation theoryφ→ φ+ const

Shift symmetry is broken to a discrete shift symmetry bynon-perturbative effects

L ⊃ 1

2(∂φ)2 + Λ4 cos

(φ

f

)⇒ φ(x)→ φ(x) + 2πf

where f is the axion decay constant and Λ ∼ e−1/g.


Axion inflation

Natural inflation [Freese et at. 90]

V (φ) = Λ4

[1 + cos

(φ

f

)],

Very hard to achieve in string theory [Banks et al. 03, Kallosh et al. 95]

Axion monodromy [(Silverstein & Westphal)(1+McAllister) 08]

V (φ) = W (φ) + Λ4 cos

(φ

f

)

Can be constructed in string theory

The hardest part is to control the large vev(e.g. backreaction on the geometry andlighter KK modes)


Inflation with more than one axion

Two axion model [Peloso et al. 04]

V = Λ41

[1 + cos

(θ

f1+

r

g1

)]+ Λ4

2

[1 + cos

(θ

f2+

r

g2

)]subplanckian axion decay constants lead to large field inflation

N-flation [Dimopoulos et al. 05] : assisted mechanism with N axions.

The vev is reduced by√N , equivalently f is enhanced by

√N


Outline

1 Motivations



4 Conclusions


Back to the Lyth bound

There is a dichotomy which becomes evident with more than oneinflaton.

The bound is on the effective inflatonφeff , i.e. the length of the inflationarytrajectory ∆φeff ≡

∫dφeff

Quantumcorrections growwith the vev’s offundamental fields.

The Lyth bound

The consequences of the Lythbound are generically differentin multi-field inflation

How complicate a potential can provide this classical trajectories?


Dante’s Inferno

The potential is as simple as this:

V (r(x), θ(x)) = W (r) + Λ4

[1− cos

(r

fr− θ

fθ

)]

Two canonically normalized axions {r, θ}, with respective axiondecay constants {fr, fθ}.The shift symmetry of r is broken by a monodromy term W (r).This could be anything. For illustration W (r) = m2r2/2.

A non-perturbative effect involves a linear combination of r and θ.

θ enjoys a shift symmetry to all order in perturbation theorybroken only by non-perturbative effects to θ → θ + 2πfθ.


The infernal potential

The potential on the two-field space

The periodicity in θ is evident in polar coordinates.

Hence the name...


Solution of the infernal dynamics

In the regime

A. fr � fθ �Mpl,

B. Λ4 � frm2r0,

r can be integrated out (mr > H), i.e. r = r(θ):

Veff (φeff) =1

2m2

eff φ2eff , meff ≡ m

frfθ

where φeff ' cos(fr/fθ)θ + sin(fr/fθ)r.


The extra dial and the η-problem

The η-problem is alleviated

Since meff = m(fr/fθ),

even if m ∼ H and hence r would have an η-problem, a mildhierachy fr/fθ ∼ O(.1) gives slow-roll inflation.

Intuitively φeff is mostly θ which has a shift symmetry.


The extra dial and the field range

What about the field range?

∆φeff ' 15Mpl, but...

whole inflationary dynamics takes place inside

0 < θ < 2πfθ , 0 < r < 15Mplfrfθ

Provided fr/fθ ∼ O(10−1 − 10−2), chaotic inflation takes place ina region subplanckian in size.


Summary of the effective model

Phenomenology:

Observable tensor modes

Oscillations in correlation functions (model dependent)[Raphael’s talk]

Inverse decay non-Gaussianity (model dependent)[Marco and Neil’s talks]

Theoretical considerations:

The inflaton is mostly an axion with a shift symmetry (onlynon-perturbative corrections) which alleviates the η-problem.

The whole large-field inflationary dynamics takes place within aregion subplanckian in size.

Issues related to the large vev’s of the axions are alleviated


Outline

1 Motivations



4 Conclusions


A cartoon of Dante’s Inferno

Two axions:two-cycles Σr and Σθ

Monodromy:NS5-branes

Non-perturbative term:Euclidean D1-brane


The setup [McAllister et al. 08]

Type IIB orientifolds.

Moduli stabilization a la KKLT does not spoil the shift symmetry.

Non-perturbative effects (e.g. ED1) and the monodromy term(5-brane) can wrap two overlapping but non-identiacal two-cycles.

We can choose a basis of two-cycles such that only one axion has amonodromy, say r

V (r(x), θ(x)) = W (r) + Λ4

[1− cos

(r

fr− θ

fθ

)]Even if W is steep, inflation works provided fr � fθ.


The axion decay constant

Using N = 1 4D data and dimensional reduction one finds

f2

M2pl

=gs

8π2

cα−−vα

VE∝ gsV4� 1

The ratio fr/fθ depends on the geometry

frfθ

=cαrrv

α

cβθθvβ

Easily O(10) or more

Axion decay constant in string theory

In controlled setups gs � 1 and L� α′, hence f �Mpl. [Banks et al. 03]


Outline

1 Motivations



4 Conclusions


Conclusions

Dante’s inferno is a robust string theory model of large fieldinflation

UV symmetries protect the flatness of the potential

The infernal dynamics ensures small vevs

Observable tensor modes (plus model dependent signals) make it afalsifiable model


based onberg, e.p. & sj ors, arxiv:0912.1341 (hep-th ...mctp/sciprgpgs/events/2011... ·...

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